Two Jobs, Often Confused
NAD+ does two completely different things, and most confusion about it comes from treating them as one.
As a cofactor it is recycled. It accepts a hydride to become NADH and is re-oxidised back, shuttling electrons through glycolysis, the TCA cycle and oxidative phosphorylation. Nothing is consumed; the pool turns over indefinitely.
As a substrate it is destroyed. Sirtuins, PARPs and CD38 cleave the nicotinamide–ribose bond, consuming NAD+ stoichiometrically and releasing nicotinamide. That consumption has to be replaced, and the replacement route is the salvage pathway.
Everything interesting about NAD+ in ageing research follows from the second job, not the first.
The Salvage Pathway in One Paragraph
Nicotinamide released by NAD+-consuming enzymes is recaptured. Nicotinamide phosphoribosyltransferase (NAMPT) converts it to nicotinamide mononucleotide (NMN), and NMN adenylyltransferases convert NMN to NAD+. That loop — consume, release nicotinamide, recapture, rebuild — is how a cell maintains its NAD+ pool without synthesising it from tryptophan every time.
The loop has a leak. Any nicotinamide diverted to something other than salvage is nicotinamide that does not come back as NAD+. That leak is where NNMT comes in.
NNMT: The Enzyme That Diverts Nicotinamide
Nicotinamide N-methyltransferase transfers a methyl group from S-adenosylmethionine to nicotinamide, producing 1-methylnicotinamide. The product is excreted rather than recycled, so every molecule NNMT processes is permanently removed from the salvage loop.
That makes NNMT an obvious target if the goal is preserving NAD+ precursor availability, and it is the mechanistic reason 5-amino-1MQ and NAD+ turn up in the same studies.
5-Amino-1MQ is a substrate-site-directed NNMT inhibitor with a reported IC50 around 1.2 µM. In 3T3-L1 adipocyte culture it has been reported to reduce lipogenesis with an EC50 near 30 µM — roughly 25-fold above the enzymatic figure, which is a gap worth designing around rather than ignoring.
NAD+ vs NMN vs NR: Not Interchangeable
Vendor literature treats these three as variants of one thing. They are not.
NAD+ is the cofactor itself, 663.43 g/mol, CAS 53-84-9. NMN is one step upstream. NR (nicotinamide riboside) is a step upstream of that and uses a different transport route into the cell.
They have different pharmacokinetics, different cell-entry mechanisms, and in several systems different effects. Substituting one for another because a supplier lists them under the same heading will produce results that do not mean what you think they mean. Decide which species your design requires before ordering.
Where Glutathione Fits
Glutathione sits adjacent to this chemistry rather than inside it, and the connection runs through NADPH.
The GSH/GSSG ratio — the standard readout of intracellular redox state — is maintained by glutathione reductase, which spends NADPH to regenerate reduced glutathione. NADPH and NAD+ are distinct pools with distinct roles, but both are nicotinamide nucleotides and both are pressured by the same metabolic demands. A study manipulating one that does not at least measure the other is leaving a variable unwatched.
Glutathione's own quirk is structural: the glutamate joins through its γ-carboxyl rather than the usual α-carboxyl, which makes the tripeptide invisible to ordinary peptidases and forces its turnover through γ-glutamyl transpeptidase at the cell surface.
Handling: The Part That Catches People Out
NAD+ is hygroscopic and hydrolyses in solution, particularly at alkaline pH, and degrades on repeated freeze–thaw. Store the powder desiccated, make solutions up immediately before use, keep them cold, and do not plan on storing a stock. This is the single most common source of irreproducible NAD+ data.
5-Amino-1MQ needs DMSO, not water. It also matters which form you have: the certificate identifies the free cation (CAS 685079-15-6, C10H11N2+, 159.21 g/mol), while the iodide salt is sometimes listed at 286.11. About 1.89 mg of the salt delivers 1 mg of the cation — ignore the counter-ion and your molar concentration is wrong by nearly a factor of two.
Glutathione's thiol oxidises in air. A purity figure is only true at the time of testing. Keep the vial sealed, prepare fresh, and where the GSH/GSSG ratio is the measurement, degas the buffer and work quickly.
Frequently Asked Questions
Is NAD+ a peptide?
No. It is a dinucleotide of 663.43 g/mol — nicotinamide riboside and adenosine joined by a pyrophosphate bridge — with no amino-acid sequence. It is stocked alongside peptides because it is used in the same laboratories and the same assays.
Can I substitute NMN or NR for NAD+?
Not without changing the experiment. They are precursors at different points in the salvage pathway, with different pharmacokinetics and different cell-entry routes. Which one you need depends on where in the pathway your question sits.
How does inhibiting NNMT raise NAD+?
Indirectly, by stopping a leak. NNMT methylates nicotinamide into a product that is excreted rather than recycled. Inhibiting it leaves more nicotinamide available to the salvage pathway, which is the route that rebuilds NAD+ after sirtuins, PARPs and CD38 consume it.
Why do NAD+ results vary between runs?
Almost always handling. NAD+ is hygroscopic, hydrolyses in aqueous solution — faster at alkaline pH — and degrades on freeze–thaw. Stored stock solutions are the usual culprit; prepare fresh each time.
References & Further Reading
Covarrubias AJ et al., Nat Rev Mol Cell Biol 2021;22:119-141; Cantó C, Menzies KJ, Auwerx J, Cell Metab 2015;22:31-53; Neelakantan H et al., Biochem Pharmacol 2017;147:141-152; Meister A, Anderson ME, Annu Rev Biochem 1983;52:711-760.